It is known that solid articles or products such as paper, films, coatings and non-sheet solids can be formed from aqueous dispersions of delaminated vermiculite ore, known as platelets or lamellae, by casting the dispersions against surfaces of various shapes and sizes and removing water from the vermiculite particles. Such dispersions can also be used to form rigid foams by gasifying the dispersion prior to removal of water from it.
Vermiculite platelets or lamellae can be characterized as tiny particles of vermiculite having a particle size typically less than 200 microns, preferably less than 50 microns, and having one dimension that is small compared to the other two dimensions. Such particles can be further characterized as having an aspect ratio (i.e., length or breadth divided by thickness) of at least 10, preferably at least 100 and more preferably at least 1,000, for example 10,000.
It is also known that vermiculite ore, a type of layer mineral (and other layer-silicate minerals containing vermiculite layers, e.g., hydrobiotite or chlorite vermiculite) can be delaminated to produce aqueous dispersions of vermiculite lamellae by first expanding or exfoliating the mineral by application of heat, or by chemical means followed by soaking or washing with water to swell the vermiculite particulate structure. The resulting expanded or swollen granules of vermiculite are then mechanically sheared to form an aqueous dispersion of vermiculite lamellae. Such processes typically involve heating the vermiculite mineral to temperatures of 1400.degree. F. or more (thermal exfoliation of vermiculite) or by treatment with hydrogen peroxide or with aqueous solutions of inorganic and/or organic salts prior to swelling and shearing the vermiculite particles (chemical delamination of vermiculite). Accordingly, such processes for the delamination of vermiculite ore and the manufacture of products therefrom are described, for example, in U.S. Pat. Nos. 4,608,303; 4,472,478; 4,271,228; 3,791,969; 3,434,917; 3,325,340; and, GB Nos. 2,007,153; 1,585,104; 1,119,305; and 1,076,786.
Delamination processes such as discussed above, however, are nondesirable from the standpoint that they require expensive and time consuming steps. For example, thermal exfoliation of vermiculite followed by mechanical shearing necessitates maintaining costly high processing temperatures, typically above 1400.degree. F., to expand the vermiculite ore. Chemical delamination of vermiculite also involves costly extra processing steps involving treatment of vermiculite ore with various chemical salt solutions. Such chemical treatment further involves more time consuming steps of washing out excess salts and swelling the vermiculite ore to at least twice its original volume prior to shearing to obtain lamellae of the desired size. Chemical delamination processes can also involve equipment corrosion problems due to the presence of high concentrations of chloride ions from salt solutions employed therein with attendant toxicity and effluent stream disposal concerns requiring extensive effluent waste stream processing. Furthermore, delamination processes such as described above can increase labor and production costs in the manufacture of paper, paper products and rigid foam articles from vermiculite ore, as drainage and production rates are decreased due to voluminous vermiculite structures produced from ore expanding and swelling steps. Finely, some chemical delamination techniques which utilize organocations to intercalate vermiculite ore and permit swelling of the ore in water may introduce a high loading of organics into the vermiculite structure therein decreasing thermal and oxidative stabilities of paper, rigid foam and non-sheet solids manufactured from such delaminated ore.
It is an object, therefore, of this invention to provide an improved process for producing dispersions of vermiculite lamellae which eliminates such costly and time consuming steps associated with thermal and chemical exfoliation and delamination as set forth above, and to produce paper, films, coatings, rigid foams and non-sheet solid articles therefrom.